In recent years, the recycling or reclamation of construction materials has become of increasing interest in view of the perceived need to conserve landfill space and non-renewable resources such as petroleum. By their nature, thermoplastic polymers are inherently recyclable in principle since they are materials with non-crosslinked macromolecular structures which will repeatedly soften when heated and reharden when cooled. Waste or scrap thermoplastic polymers thus may theoretically be reshaped into useful molded articles. In practice, however, great care must be taken to segregate waste streams by polymer type since the presence of even minor amounts of one polymer in another may significantly degrade the physical and mechanical properties of the dominant polymer. Polymeric contaminants thus frequently prevent recycled polymers from being used interchangeably with virgin resins due to their adverse effect on quality.
An example of this is found in the reclamation of interior trim parts from automobiles and other vehicles which have been produced using a heat resistant polymer such as a styrene maleic anhydride copolymer or polyphenylene ether. It is common practice to place an outer skin on instrument panels and the like to enhance appearance. An intermediate layer such as a urethane foam may also be present to provide padding. The outer skin differs in composition from the underlying substrate and frequently contains a vinyl chloride polymer such as polyvinyl chloride compounded with plasticizers, colorants, and other additives. After the trimming operations common to instrument panel manufacture or after the instrument panel has been removed from the vehicle at the end of its useful service life, the heat resistant polymer could in theory be formed into new trim parts by grinding or chopping into small particles and then remolding those particles by injection molding techniques. However, it is exceedingly difficult to remove essentially all of the outer skin from the trim part prior to such reuse through the use of solvent or mechanical separation means. The heat resistant polymer thus, for all practical purposes, is invariably contaminated with small amounts of polyvinyl chloride.
Such contamination makes direct recycling of the heat resistant polymer impractical. The heat resistant polymer must be processed and molded at relatively high temperatures. The vinyl chloride polymer contaminant is unstable at such elevated temperatures and tends to thermally degrade. This degradation adversely affects certain physical properties of the heat resistant thermoplastic polymer such as tensile strength/toughness and flex strength/toughness. Moreover, the acidic byproducts generated by the degradation of the vinyl chloride polymer accelerate machine and mold wear.
As a result, there exists a need for methods whereby a heat resistant thermoplastic polymer contaminated with a vinyl chloride polymer such as polyvinyl chloride may be processed to provide a recycled resin composition at least equivalent in performance to non-contaminated polymer.